The embodiments described herein relate generally to gas turbine engines, and more particularly, to a turbine bucket used with gas turbine engines.
At least some known gas turbine engines include a combustor, a compressor coupled downstream from the combustor, a turbine, and a rotor assembly rotatably coupled between the compressor and the turbine. At least some known rotor assemblies include a rotor shaft, at least one rotor disk coupled to the rotor shaft, and a plurality of circumferentially-spaced turbine buckets that are coupled to each rotor disk. Each turbine bucket includes an airfoil that extends radially outward from a platform towards a turbine casing.
During operation of at least some known turbines, the compressor compresses air, which is mixed with fuel and channeled to the combustor. The mixture is then ignited generating hot combustion gases that are then channeled to the turbine. The rotating turbine blades or buckets channel high-temperature fluids, such as combustion gases, through the turbine. The turbine extracts energy from the combustion gases for powering the compressor, as well as producing useful work to power a load, such as an electrical generator, or to propel an aircraft in flight.
At least some known gas turbine engines include Nickel based super alloys for the manufacture of advanced hot gas turbine blades. These blades need to be cooled in order to withstand the operating temperatures of combustion gases. This cooling flow is detrimental to the engine performance as it is not used to generate power at its most useful pressure and temperature state. Ceramic Matrix Composite (CMCs) materials could reduce, or eliminate, cooling flows due to their temperature resistance. These materials are sensitive to any sort of impact however, which requires the tip clearance between the casing and the blade to be increased due to rub events, which could prove catastrophic to the integrity of a blade. Increasing the clearance between the casing and the blade introduces tip leakage losses (also, clearance loss).
At least a portion of combustion gases channeled through at least some known turbines are channeled between a tip end of the airfoil and a turbine casing as tip clearance losses. Such tip clearance loses reduce the amount of combustion gases that is channeled through the main flow path and reduce an operating efficiency of the turbine.